Variation in Pathogenicity, Virulence, and Aggressiveness ofSeptoria nodorumin Florida

Abstract

Pathogenicity, virulence and aggressiveness of 282 isolates of S. nodorum, causal agent of glume blotch of wheat [Triticum aestivum], were determined on 8 wheat cultivars of varying resistance. Cultivar reactions, measured as percentage necrosis of seedling leaves, were classified into 253 different resistance patterns. Ninety-five isolates were pathogenic to all 8 cultivars; 85, to 7; 54, to 6; 32, to 5; 11, to 4; 4, to 3, and 1, to 2 cultivars. An isolate was considered pathogenic if it caused necrosis in a greenhouse test. Virulence of the isolates varied; maximum necrosis induced in the cultivars after 12 days ranged 13-80.degree. C Isolates from commercial fields were less variable in pathogenicity and more virulent than those from research plots. Aggressiveness, measured as the time to produce the 1st necrosis on seedling leaves of the cv. Potomac, ranged 3 to 10 days after inoculation. Pathogenic and virulent types were present in differing frequencies and distributions in subpopulations defined in terms of geographic origin and year of isolation.